linux-kernel - Re: [PATCH] kvm: fix hyperv tsc page clear wrong address

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Message-ID: <53A2C7F9.8070700@redhat.com>
Date:	Thu, 19 Jun 2014 13:22:33 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"newtongao(高小明)" 
	<gxm.linux.kernel@...il.com>, gleb@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com
CC:	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: fix hyperv tsc page clear wrong address

Il 19/06/2014 13:17, "newtongao(高小明)" ha scritto:
> This is more concisely
>
> From 6ddeb18347f9dda0fe37702e0d067a4129a89b54 Mon Sep 17 00:00:00 2001
> From: Xiaoming Gao <newtongao@...cent.com>
> Date: Thu, 19 Jun 2014 19:14:57 +0800
> Subject: [PATCH] kvm: fix hyperv tsc page clear wrong address
>
> tsc page addr need clear the low HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT bits
> before kvm_write_guest write the zero tsc_ref structure to guest, or it will lead
> guest to get wrong clocksource.
>
> windows guest will get strong impact, QueryPerformanceCounter will always return 0
> ,all things in windows rely on clock source, will in serious chaos.

Right, this can happen if Windows passes a non-zero page to KVM.

Thanks,

Paolo

> Signed-off-by: Xiaoming Gao <newtongao@...cnet.com>
> ---
>  arch/x86/kvm/x86.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f32a025..f644933 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1898,7 +1898,7 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  		if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE))
>  			break;
>  		gfn = data >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
> -		if (kvm_write_guest(kvm, data,
> +		if (kvm_write_guest(kvm, gfn << HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT,
>  			&tsc_ref, sizeof(tsc_ref)))
>  			return 1;
>  		mark_page_dirty(kvm, gfn);
>

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